PROJECT SUMMARY/ABSTRACT Neuroblastoma is the most common solid tumor in early childhood. Neuroblastoma due to MYCN oncogene amplification and consequent N-Myc oncoprotein over-expression represent the worst subtype of the disease. Although >10,000 human long noncoding RNAs (lncRNAs) have been manually annotated or predicted by bioinformatics analysis, less than 1% of human lncRNAs have been functionally characterized. We have recently performed RNA sequencing experiments, and identified RP1X as one of the few transcripts most dramatically up-regulated in MYCN gene amplified, compared with MYCN non-amplified, human neuroblastoma cell lines. While RP1X has never been studied in normal biology or any disease, our Affymetrix microarray, RNA-binding protein pull-down assays and mass spectrometry analysis identified RP1X target genes and its binding protein. Importantly, knocking down RP1X abolished clonogenic capacity of neuroblastoma cells in vitro, and led to tumor regression or eradication in neuroblastoma-bearing mice. In a cohort of 498 neuroblastoma patients, high levels of RP1X, its target gene and its binding protein expression in tumor tissues correlated with poor prognosis. Specific Aims. (1) To identify the mechanism through which the novel long noncoding RNA RP1X induces N- Myc protein stabilization; (2) To identify the role of RP1X in neuroblastoma tumorigenesis in vivo. (3) To identify approved drugs and small molecule compounds which block RP1X RNA interaction with its binding protein, and to examine their anticancer efficacy in vitro and in mice. Outcomes and Significance. This project will demonstrate that (i) the novel long noncoding RNA RP1X increases N-Myc oncoprotein stability by interacting with its binding protein, (ii) RP1X induces neuroblastoma tumorigenesis in mice, and (iii) approved drugs and small molecule compounds which block RP1X interaction with its binding protein will be identified by approved drug and small molecule compound library AlphaScreening, and their anticancer effects against neuroblastoma in vitro and in vivo will be demonstrated. Successful completion of this project will provide the first evidence for the role of RP1X in N-Myc protein stabilization and neuroblastoma tumorigenesis, and identify a novel therapeutic strategy against neuroblastoma. As aberrant long noncoding RNA expression is a common feature of human cancers, this project will provide the first example for targeting long noncoding RNAs for cancer therapy by blocking their interaction with binding proteins with approved drugs and small molecule compounds.